The northern part of the Indus Valley, with its tributaries, forms the Punjab region, while the lower course of the river is known as Sindh and ends in a large delta. The river has historically been important to many cultures of the region. The 3rd millennium BC saw the rise of a major urban civilization of the Bronze Age. During the 2nd millennium BC, the Punjab region was mentioned in the hymns of the HinduRigveda as Sapta Sindhu and the ZoroastrianAvesta as Hapta Hindu (both terms meaning "seven rivers"). Early historical kingdoms that arose in the Indus Valley include Gandhāra, and the Ror dynasty of Sauvīra. The Indus River came into the knowledge of the West early in the Classical Period, when King Darius of Persia sent his Greek subject Scylax of Caryanda to explore the river, c. 515 BC.

The meaning of Sindhu as a "large body of water, sea, or ocean" is a later meaning in Classical Sanskrit.[13] A later Persian name for the river was Darya,[14] which similarly has the connotations of large body of water and sea.[citation needed] Other variants of the name Sindhu include AssyrianSinda (as early as the 7th century BC), Persian Ab-e-sind, Pashto Abasind, Arab Al-Sind, Chinese Sintow, and Javanese Santri.[citation needed]

The Indus River provides key water resources for Pakistan's economy ��� especially the breadbasket of Punjab province, which accounts for most of the nation's agricultural production, and Sindh. The word Punjab means "land of five rivers" and the five rivers are Jhelum, Chenab, Ravi, Beas and Sutlej, all of which finally flow into the Indus. The Indus also supports many heavy industries and provides the main supply of potable water in Pakistan.

The ultimate source of the Indus is in Tibet; the river begins at the confluence of the Sengge Zangbo and Gar Tsangpo rivers that drain the Nganglong Kangri and Gangdise Shan (Gang Rinpoche, Mt. Kailash) mountain ranges. The Indus then flows northwest through Ladakh, India, and Baltistan into Gilgit, just south of the Karakoram range. The Shyok, Shigar and Gilgit rivers carry glacial waters into the main river. It gradually bends to the south and descends into the Punjab plains at Kalabagh, Pakistan. The Indus passes gigantic gorges 4,500–5,200 metres (15,000–17,000 feet) deep near the Nanga Parbatmassif. It flows swiftly across Hazara and is dammed at the Tarbela Reservoir. The Kabul River joins it near Attock. The remainder of its route to the sea is in the plains of the Punjab[15] and Sindh, where the flow of the river becomes slow and highly braided. It is joined by the Panjnad at Mithankot. Beyond this confluence, the river, at one time, was named the Satnad River (sat = "seven", nadī = "river"), as the river now carried the waters of the Kabul River, the Indus River and the five Punjab rivers. Passing by Jamshoro, it ends in a large delta to the South of Thatta in the Sindh province of Pakistan

The Indus is one of the few rivers in the world to exhibit a tidal bore. The Indus system is largely fed by the snows and glaciers of the Himalayas, Karakoram and the Hindu Kush ranges of Tibet, the Indian states and union territories of Ladakh and Himachal Pradesh and the Gilgit-Baltistan region of Pakistan. The flow of the river is also determined by the seasons – it diminishes greatly in the winter, while flooding its banks in the monsoon months from July to September. There is also evidence of a steady shift in the course of the river since prehistoric times – it deviated westwards from flowing into the Rann of Kutch and adjoining Banni grasslands after the 1816 earthquake.[16][17] Presently, Indus water flows in to the Rann of Kutch during its floods breaching flood banks.[18]

The traditional source of the river is the Sênggê Kanbab (a.k.a. Sênggê Zangbo, Senge Khabab) or "Lion's Mouth", a perennial spring, not far from the sacred Mount Kailash marked by a long low line of Tibetan chortens. There are several other tributaries nearby, which may possibly form a longer stream than Sênggê Kanbab, but unlike the Sênggê Kanbab, are all dependent on snowmelt. The Zanskar River, which flows into the Indus in Ladakh, has a greater volume of water than the Indus itself before that point.[19]

The major cities of the Indus Valley Civilisation, such as Harappa and Mohenjo-daro, date back to around 3300 BC, and represent some of the largest human habitations of the ancient world. The Indus Valley Civilisation extended from across northeast Afghanistan to Pakistan and northwest India,[20] with an upward reach from east of Jhelum River to Ropar on the upper Sutlej. The coastal settlements extended from Sutkagan Dor at the Pakistan, Iran border to Kutch in modern Gujarat, India. There is an Indus site on the Amu Darya at Shortughai in northern Afghanistan, and the Indus site Alamgirpur at the Hindon River is located only 28 km (17 mi) from Delhi. To date, over 1,052 cities and settlements have been found, mainly in the general region of the Ghaggar-Hakra River and its tributaries. Among the settlements were the major urban centres of Harappa and Mohenjo-daro, as well as Lothal, Dholavira, Ganeriwala, and Rakhigarhi. Only 90–96 of more than 800 known Indus Valley sites have been discovered on the Indus and its tributaries.[citation needed] The Sutlej, now a tributary of the Indus, in Harappan times flowed into the Ghaggar-Hakra River, in the watershed of which were more Harappan sites than along the Indus.

The Rigveda describes several rivers, including one named "Sindhu". The Rigvedic "Sindhu" is thought to be the present-day Indus river. It is attested 176 times in its text, 94 times in the plural, and most often used in the generic sense of "river". In the Rigveda, notably in the later hymns, the meaning of the word is narrowed to refer to the Indus river in particular, e.g. in the list of rivers mentioned in the hymn of Nadistuti sukta. The Rigvedic hymns apply a feminine gender to all the rivers mentioned therein, except for the Brahmaputra.

The word "India" is derived from the Indus River. In ancient times, "India" initially referred to those regions immediately along the east bank of the Indus, but by 300 BC, Greek writers including Herodotus and Megasthenes were applying the term to the entire subcontinent that extends much farther eastward.[21][22]

Confluence of Indus and Zanskar rivers. The Indus is at the left of the picture, flowing left-to-right; the Zanskar, carrying more water, comes in from the top of the picture.

The Indus river feeds the Indus submarine fan, which is the second largest sediment body on the Earth.[23] It consists of around 5 million cubic kilometres of material eroded from the mountains. Studies of the sediment in the modern river indicate that the Karakoram Mountains in northern Pakistan and India are the single most important source of material, with the Himalayas providing the next largest contribution, mostly via the large rivers of the Punjab (Jhelum, Ravi, Chenab, Beas and Sutlej). Analysis of sediments from the Arabian Sea has demonstrated that prior to five million years ago the Indus was not connected to these Punjab rivers which instead flowed east into the Ganga and were captured after that time.[24] Earlier work showed that sand and silt from western Tibet was reaching the Arabian Sea by 45 million years ago, implying the existence of an ancient Indus River by that time.[25] The delta of this proto-Indus river has subsequently been found in the Katawaz Basin, on the Afghan-Pakistan border.

In the Nanga Parbat region, the massive amounts of erosion due to the Indus river following the capture and rerouting through that area is thought to bring middle and lower crustal rocks to the surface.[26]

Accounts of the Indus valley from the times of Alexander's campaign indicate a healthy forest cover in the region, which has now considerably receded. The Mughal Emperor Babur writes of encountering rhinoceroses along its bank in his memoirs (the Baburnama). Extensive deforestation and human interference in the ecology of the Shivalik Hills has led to a marked deterioration in vegetation and growing conditions. The Indus valley regions are arid with poor vegetation. Agriculture is sustained largely due to irrigation works.
The Indus river and its watershed has a rich biodiversity. It is home to around 25 amphibian species.[27]

There are two otter species in the Indus River basin: the Eurasian otter in the northeastern highland sections and the smooth-coated otter elsewhere in the river basin. The smooth-coated otters in the Indus River represent a subspecies found nowhere else, the Sindh otter (Lutrogale perspicillata sindica).[29]

The Indus River basin has a high diversity, being the home of more than 180 freshwater fish species,[30] including 22 which are found nowhere else.[27] Fish also played a major role in earlier cultures of the region, including the ancient Indus Valley Civilisation where depictions of fish were frequent. The Indus script has a commonly used fish sign, which in its various forms may simply have meant "fish", or referred to stars or gods.[31]

Palla fish (Tenualosa ilisha) of the river is a delicacy for people living along the river. The population of fish in the river is moderately high, with Sukkur, Thatta, and Kotri being the major fishing centres – all in the lower Sindh course. As a result, damming and irrigation has made fish farming an important economic activity.

The Indus is the most important supplier of water resources to the Punjab and Sindh plains – it forms the backbone of agriculture and food production in Pakistan. The river is especially critical since rainfall is meagre in the lower Indus valley. Irrigation canals were first built by the people of the Indus Valley Civilisation, and later by the engineers of the Kushan Empire and the Mughal Empire. Modern irrigation was introduced by the British East India Company in 1850 – the construction of modern canals accompanied with the restoration of old canals. The British supervised the construction of one of the most complex irrigation networks in the world. The Guddu Barrage is 1,350 m (4,430 ft) long – irrigating Sukkur, Jacobabad, Larkana and Kalat. The Sukkur Barrage serves over 20,000 km2 (7,700 sq mi).

The Indus Basin Project consisted primarily of the construction of two main dams, the Mangla Dam built on the Jhelum River and the Tarbela Dam constructed on the Indus River, together with their subsidiary dams.[33] The Pakistan Water and Power Development Authority undertook the construction of the Chashma-Jhelum link canal – linking the waters of the Indus and Jhelum rivers – extending water supplies to the regions of Bahawalpur and Multan. Pakistan constructed the Tarbela Dam near Rawalpindi – standing 2,743 metres (9,000 ft) long and 143 metres (470 ft) high, with an 80-kilometre (50 mi) long reservoir. It supports the Chashma Barrage near Dera Ismail Khan for irrigation use and flood control and the Taunsa Barrage near Dera Ghazi Khan which also produces 100,000 kilowatts of electricity. The Kotri Barrage near Hyderabad is 915 metres (3,000 ft) long and provides additional water supplies for Karachi. The extensive linking of tributaries with the Indus has helped spread water resources to the valley of Peshawar, in the Khyber Pakhtunkhwa. The extensive irrigation and dam projects provide the basis for Pakistan's large production of crops such as cotton, sugarcane and wheat. The dams also generate electricity for heavy industries and urban centers.

The inhabitants of the regions are mainly Muslim as Pakistan is an Islamic country through which the Indus river passes and forms a major natural feature and resource are diverse in ethnicity, religion, national and linguistic backgrounds. On the northern course of the river in the union territory of Ladakh in India, live the Buddhist people of Ladakh, of Tibetan stock, and the Dards of Indo-Aryan or Dardic stock and practising Islam. Then it descends into Baltistan, northern Pakistan passing the main Balti city of Skardu. A river from Dubair Bala also drains into it at Dubair Bazar. People living in this area are mainly Kohistani and speak the Kohistani language. Major areas through which the Indus river passes in Kohistan are Dasu, Pattan and Dubair. As it continues through Pakistan, the Indus river forms a distinctive boundary of ethnicity and cultures – upon the western banks the population is largely Pashtun, Baloch, and of other Iranian stock. The eastern banks are largely populated by people of Indo-Aryan stock, such as the Punjabis and the Sindhis. In northern Punjab and the Khyber Pakhtunkhwa, ethnic Pashtun tribes live alongside Dardic people in the hills (Khowar, Kalash, Shina, etc.), Burushos (in Hunza), and Punjabi people.

The people living along the Indus river speak Punjabi and Sindhi on the eastern side (in Punjab and Sindh provinces respectively), Pushto plus Balochi as well as Barohi (in Khyber Pakhtoonkha and Baluchistan provinces). In the province of Sindh, the upper third of the river is inhabited by people speaking Saraiki; which is a somewhat transitional dialect of the Punjabi and Sindhi languages.

The ethnicities of the Indus Valley (Pakistan and Northwest India) have a greater amount of ANI (or West Eurasian) admixture than other South Asians, including inputs from Western Steppe Herders, with evidence of more sustained and multi-layered migrations from the west.[34]

Satellite images of the upper Indus River valley, comparing water-levels on 1 August 2009 (top) and 31 July 2010 (bottom)

The Indus is a strategically vital resource for Pakistan's economy and society. After Pakistan and India declared Independence from the British Raj, the use of the waters of the Indus and its five eastern tributaries became a major dispute between India and Pakistan. The irrigation canals of the Sutlej valley and the Bari Doab were split – with the canals lying primarily in Pakistan and the headwork dams in India disrupting supply in some parts of Pakistan. The concern over India building large dams over various Punjab rivers that could undercut the supply flowing to Pakistan, as well as the possibility that India could divert rivers in the time of war, caused political consternation in Pakistan. Holding diplomatic talks brokered by the World Bank, India and Pakistan signed the Indus Waters Treaty in 1960. The treaty gave India control of the three easternmost rivers of the Punjab, the Sutlej, the Beas and the Ravi, while Pakistan gained control of the three western rivers, the Jhelum, the Chenab and the Indus. India retained the right to use of the western rivers for non-irrigation projects.[citation needed]

Large-scale diversion of the river's water for irrigation has raised far-reaching issues. Sediment clogging from poor maintenance of canals has affected agricultural production and vegetation on numerous occasions. Irrigation itself is increasing soil salinization, reducing crop yields and in some cases rendering farmland useless for cultivation.[35] And ecologically, the reduced flow of fresh water and silt into the Indus delta is threatening the area's mangrove forests.[citation needed]

There are also concerns that the Indus River may be shifting its course westwards, although the progression spans centuries.

Originally, the delta used to receive almost all of the water from the Indus river, which has an annual flow of approximately 180 billion cubic metres (240 billion cubic yards), and is accompanied by 400 million tonnes (390 million long tons) of silt.[36] Since the 1940s, dams, barrages and irrigation works have been constructed on the river Indus. The Indus Basin Irrigation System is the "largest contiguous irrigation system developed over the past 140 years" anywhere in the world.[37] This has reduced the flow of water and by 2018, the average annual flow of water below the Kotri barrage was 33 billion cubic metres (43 billion cubic yards),[38] and annual amount of silt discharged was estimated at 100 million tonnes (98 million long tons).[citation needed] As a result, the 2010 Pakistan floods were considered "good news" for the ecosystem and population of the river delta as they brought much needed fresh water.[39][40] Any further utilization of the river basin water is not economically feasible.[41][42]

Vegetation and wildlife of the Indus delta are threatened by the reduced inflow of fresh water, along with extensive deforestation, industrial pollution and global warming. Damming has also isolated the delta population of Indus river dolphins from those further upstream.[43]

The Tibetan Plateau contains the world's third-largest store of ice. Qin Dahe, the former head of the China Meteorological Administration, said the recent fast pace of melting and warmer temperatures will be good for agriculture and tourism in the short term, but issued a strong warning:

"Temperatures are rising four times faster than elsewhere in China, and the Tibetan glaciers are retreating at a higher speed than in any other part of the world... In the short term, this will cause lakes to expand and bring floods and mudflows.. In the long run, the glaciers are vital lifelines of the Indus River. Once they vanish, water supplies in Pakistan will be in peril."[44]

"There is insufficient data to say what will happen to the Indus," says David Grey, the World Bank's senior water advisor in South Asia. "But we all have very nasty fears that the flows of the Indus could be severely, severely affected by glacier melt as a consequence of climate change," and reduced by perhaps as much as 50 percent. "Now what does that mean to a population that lives in a desert [where], without the river, there would be no life? I don't know the answer to that question," he says. "But we need to be concerned about that. Deeply, deeply concerned."

U.S. diplomat Richard Holbrooke said, shortly before his death in 2010, that he believed that falling water levels in the Indus River "could very well precipitate World War III."[45]

Over the years factories on the banks of the Indus River have increased levels of water pollution in the river and the atmosphere around it. High levels of pollutants in the river have led to the deaths of endangered Indus river dolphin. The Sindh Environmental Protection Agency has ordered polluting factories around the river to shut down under the Pakistan Environmental Protection Act, 1997.[46] Death of the Indus river dolphin has also been attributed to fishermen using poison to kill fish and scooping them up.[47][48] As a result, the government banned fishing from Guddu Barrage to Sukkur.[49]

The Indus is second among a group of ten rivers responsible for about 90% of all the plastic that reaches the oceans. The Yangtze is the only river contributing more plastic.[50][51]

Frequently, Indus river is prone to moderate to severe flooding.[52] In July 2010, following abnormally heavy monsoon rains, the Indus River rose above its banks and started flooding. The rain continued for the next two months, devastating large areas of Pakistan. In Sindh, the Indus burst its banks near Sukkur on 8 August, submerging the village of Mor Khan Jatoi.[53] In early August, the heaviest flooding moved southward along the Indus River from severely affected northern regions toward western Punjab, where at least 1,400,000 acres (570,000 ha) of cropland was destroyed, and the southern province of Sindh.[54] As of September 2010[update], over two thousand people had died and over a million homes had been destroyed since the flooding began.[55][56]

The 2011 Sindh floods began during the Pakistani monsoon season in mid-August 2011, resulting from heavy monsoon rains in Sindh, eastern Balochistan, and southern Punjab.[57] The floods caused considerable damage; an estimated 434 civilians were killed, with 5.3 million people and 1,524,773 homes affected.[58] Sindh is a fertile region and often called the "breadbasket" of the country; the damage and toll of the floods on the local agrarian economy was said to be extensive. At least 1.7 million acres (690,000 ha; 2,700 sq mi) of arable land were inundated. The flooding followed the previous year's floods, which devastated a large part of the country.[58] Unprecedented torrential monsoon rains caused severe flooding in 16 districts of Sindh.[59]

In Pakistan currently there are six barrages on the Indus: Guddu barrage, Sukkur Barrage, Kotri barrage (also called Ghulam Muhammad barrage), Taunsa Barrage, Chashma Barrage and Jinnah Barrage. Another new barrage called "Sindh barrage" is planned as terminal barrage on Indus River.[60] There are some bridges on river Indus, such as, Dadu Moro Bridge, Larkana Khairpur Indus River Bridge, Thatta-Sujawal bridge, Jhirk-Mula Katiar bridge and recently planned Kandhkot-Ghotki bridge.[61]

The entire left bank of Indus river in Sind province is protected from river flooding by constructing around 600 km long levees. The right bank side is also leveed from Guddu barrage to Lake Manchar.[62] In response to the levees construction, the river has been aggrading rapidly over the last 20 years leading to breaches upstream of barrages and inundation of large areas.[63]

Tarbela Dam in Pakistan is constructed on the Indus River, while the controversial Kalabagh dam is also being constructed on Indus river. Pakistan is also building Munda Dam.

^Thieme, P. (1970), "Sanskrit sindu-/Sindhu- and Old Iranian hindu-/Hindu-", in Mary Boyce; Ilya Gershevitch (eds.), W. B. Henning memorial volume, Lund Humphries, p. 450: "As the great frontier river that represents the natural dividing line between India and Iran, the Indus could most easily and fittingly be called Sindhu- 'Frontier' by the Indians and Hindu- 'Frontier' by the Iranians."

^Bailey, H. W. (1975), "Indian Sindhu-, Iranian Hindu- (Notes and Communications)", Bulletin of the School of Oriental and African Studies, 38 (3): 610–611, doi:10.1017/S0041977X00048138, JSTOR613711: "The word sindhu- is used of a 'mass of water' (samudra-), not therefore primarily 'flowing' water. Hence the second derivation of 'enclosed banks' is clearly preferable."

^Mukherjee, Bratindra Nath (2001), Nationhood and Statehood in India: A historical survey, Regency Publications, p. 3, ISBN978-81-87498-26-1: "Apparently the same territory was referred to as Hi(n)du(sh) in the Naqsh‐i‐Rustam inscription of Darius I as one of the countries in his empire.[10] The terms Hindu and India ('Indoi) indicate an original indigenous expression like Sindhu. The name Sindhu could have been pronounced by the Persians as Hindu (replacing s by h and dh by d) and the Greeks would have transformed the latter as Indo‐ (Indoi, Latin Indica, India) with h dropped..."